1. Field of the Invention
The present invention relates generally to a valve having relatively movable disk members each with at least one fluid opening which can be brought into and out of fluid conducting alignment for discharging fluid to a discharge port, and, more particularly, to improvements to such a valve which include disk members having fluid openings of a particular shape for increasing the valve turn-down ratio and flow capacity and for reducing fluid erosion in the valve especially when the valve is subjected to high fluid pressures.
2. Description of the Prior Art
This invention relates to a valve of the type having a stationary disk and a rotatable disk mounted in a valve housing in a face-to-face confronting relationship in a pathway for fluid ia valve body. The disks are each provided with at least one orifice or opening which controls the flow of fluid through the valve by the size of the openings in the disk as well as the degree of alignment between the openings in the disk. Angular movement of one disk relative to the other in the valve body is usually accomplished by moving or turning a handle situated outside of the valve body but coupled to produce rotation of the rotatable disk. The rotatable disk can be moved from a full open position wherein the opening or openings in one disk completely align with the opening or openings in the other disk for providing maximum flow through the valve to a fully closed position wherein the opening or openings in the respective disks are completely misaligned and blocked by solid portions of the confronting disks. Examples of valves which operate in this fashion are disclosed in my prior U.S. Pat. No. and 4,901,977 and in my copending U.S. patent applications Ser. Nos. 450,549 and 417,064, the disclosures of which are incorporated herein by reference.
Valves of this type are particularly useful for controlling the flow of fluids from oil and gas wells and the like. Such a valve is sometimes called a choke when used to control the rate of flow of well production fluids that may contain abrasive contaminants such as sand particles. The fluid entering the valve may be under extreme pressure of the order of, for example, 3000 PSI. The openings in the disks are of a smaller cross-sectional area than either an upstream entry chamber or a downstream discharge chamber that are formed in a valve body. The openings in the disks cause an acceleration of the fluid passing through the openings in the disk. Therefore, the fluid emerging from the opening in the downstream disk enters a discharge chamber at an increased velocity which has a cross-sectional area that is greater than the cross-sectional area of the openings in the disk, but because of the construction of the discharge chamber, particularly when provided with a replaceable protective sleeve or insert in the valve body, a large pressure drop in the fluid passing through the sleeve is created. The effect is to reduce the capacity of the valve, and depending upon the construction of the removable sleeve, abrupt changes to the configuration of the opening in the sleeve may produce turbulence in the fluid, particularly at the outlet of the valve which is unprotected by the removable sleeve.
In a known form of valve of the type under discussion as disclosed in my U.S. Pat. No. 4,603,834, the outlet is defined by an oblong transverse configuration immediately downstream of the downstream disk. The oblong configuration is a result of the need to provide openings to receive retainer pins which are used to anchor the downstream disk to the valve body. At times when a protective sleeve is required for the outlet chamber, the area of the oblong configuration is reduced by the thickness of the sleeve. The further reduced oblong area of the outlet, in turn, limits the maximum size of the disk that can be used in conjunction with the removable sleeve as compared with, for example, the size of the oblong outlet chamber when a removable sleeve is not used. The smaller volume for conducting fluid in the sleeve creates a larger pressure drop to the fluid passing through the sleeve, and thus reduces the capacity of the valve.
Moreover, in the known form of valves using replaceable sleeves at the outlet chamber, the sleeve is typically adhered to the valve body by an adhesive, such as epoxy cement, which also is relied upon to prevent the flow of fluid between the sleeve and the valve body. When it is necessary to replace the sleeve, the valve body must be heated to a temperature sufficient to soften the epoxy so that the sleeve can be removed. Typically, it is known to heat a valve body to over 250 degrees Fahrenheit in order to effectively soften the epoxy for replacement of the sleeve.
An inherent and historic disadvantage of such multiple orifice valves is that when the disks are subject to extreme pressures they are readily susceptible to damage and possible destruction if the fluid flow is required to be rapidly and significantly reduced such as, for example, during times of emergency. In such instances, the fluid openings in the disks are usually brought rapidly from a condition of complete alignment (full flow) to a maximum permissible degree of partial misalignment (minimum partial flow) wherein the misalignment of the fluid openings causes a sudden constriction of the fluid flow path and a corresponding increase in the already high fluid pressure exerted upon the disks. Furthermore, when operating under extremely high fluid pressures and a situation arises requiring that the fluid flow through the valve be reduced, it is imperative that the disks not be rapidly brought into a condition of complete misalignment, thereby ceasing fluid flow, since the sudden and large increase in fluid pressure creates an impulsive fluid shock force at the upstream disk which will almost certainly destroy the disks.
Consequently, valves of this nature, along with being normally characterized by physical and performance specifications including, inter alia, disk fluid opening size, maximum flow capacity and maximum operating pressure, are limited in their shut-down procedures by an inherent definitive safety parameter known as "turn-down ratio". The "turn-down ratio" of a multiple orifice valve is the ratio of full open flow area a minimum safe flow area to which the full open flow area can be rapidly yet safely reduced without causing damage to the disks and/or other elements of the valve. Once the valve has established equilibrium at minimum partial flow, it can usually then be gradually completely shut down by turning the movable disk such that its fluid opening(s) are in complete misalignment with those of the stationary disk.
In a conventional multiple orifice valve having circular shaped openings in the disks such as, for example, the valve disclosed in U.S. Pat. No. 3,207,181, or circular sector shaped openings in the disks such as in my aforementioned U.S. Pat. No. 4,603,834, the turn-down ratio is about 4:1. That is to say, the valve can be rapidly and safely turned down in a single step from 100% flow to about 25% flow without causing damage to the valve. Such a turn-down ratio may be acceptable for situations wherein up to 25% flow is permitted prior to complete shut-down of a valve such as, for example, during normal pipeline or valve maintenance. However, during emergency situations wherein it is essential to rapidly reduce and then cease flow through the valve in the shortest possible period of time, a turn-down ratio of 4:1 is unsatisfactory.
A secondary disadvantage associated with conventional multiple orifice valves having circular or circular sector shape fluid openings in the disks is that as the fluid openings between the stationary and movable disks become increasingly misaligned during a flow reduction operation, the common fluid passageway formed by the overlap of the fluid openings becomes increasingly slit-like in shape which creates a highly pressurized, knife-like and sharply angled discharge flow which can be severely erosive to valve components downstream of the disks, particularly if the fluid contains abrasive contaminants.
An advantage exists, therefore, for a multiple orifice valve construction capable of producing a high turn-down ratio and a minimally erosive discharge flow during conditions of reduced flow through the valve.
It is therefore an object of the present invention to provide a multiple orifice valve construction including a stationary disk and an abutting movable disk which is capable of producing a high turn-down ratio.
It is a further object of the invention to provide a multiple orifice valve construction including a stationary disk and a movable disk which is capable of producing a minimally erosive discharge flow during conditions of reduced flow through the valve.
It is a further object of the present invention to provide a multiple orifice valve construction which is advantageously used in the manufacture of new valves as well as in retrofitting existing valve assemblies.
Still other objects and advantages will become apparent in light of the attached drawings and written description of the invention presented hereinbelow.